In a wireless communication system comprising a plurality of basic service sets (BSSs), an access point (AP) of a BSS is at times required to listen to data packets transmitted from neighboring BSSs. In addition, an AP may be required to measure the level of external interference in different channels for the purpose of supporting advanced RRM functions such as frequency selection, load balancing or power management. However, an AP must also support transmission and reception of packets to and from wireless transmit/receive units (WTRUs) in its own BSS. The frequency channel used by an AP to communicate with WTRUs in its own BSS may be different from any of the frequency channels used by neighboring BSSs, or from channels on which external interference is measured.
Due to cost limitations, many APs include only one receiver. As a result, it is not possible to simultaneously measure external interference or listen to packets transmitted from other BSSs on one frequency channel and communicate with WTRUs in the AP's own BSS when it is operating on a different frequency channel. Even if an AP's own BSS operates on the same frequency channel on which measurements are to be made, these measurements may be difficult to perform if the traffic in the AP's BSS is heavy.
Accordingly, it is desirable to have a mechanism by which an AP could measure external interference and packets transmitted from neighboring BSSs, including those operating on other frequency channels, with minimal disruption of the AP's communications with WTRUs in its own BSS.